The present invention relates to lawn mowers and in particular to lawn mowers mounted on castor wheels.
A conventional rotary lawn mower comprises a cutting deck mounted on wheels and/or rollers. A motor, which can be either an electric motor or an internal combustion engine, is mounted on the cutting deck and which rotationally drives a cutting blade mounted below the cutting deck about a substantially vertical axis of rotation. A handle is attached to the rear of the cutting deck to enable an operator to maneuver the mower. Often a grass collection box is also attached to the rear of the cutting deck to collect the grass cuttings generated by the mower when in use.
In common designs mower the wheels have a direction of travel which is fixed in a forward and rearward direction. Thus the mower is able to be pushed or pulled in a forward or rearward direction, which is particularly desirable when an operator wishes to operate the mower in straight lines, for instance to generate stripes on a lawn. However, such a design of mower is unable to change direction easily. In order for the direction of travel to be altered, the operator must raise either the front or rear wheels above the ground and rotate the mower to the new direction of travel before then lowering the wheels in order to re-engage the ground. This requires a substantial effort on the part of the operator. Furthermore, the direction of travel of the mower while cutting the grass still remains in a fixed forward/rearward direction which may not be desirable in certain circumstances.
One previously proposed method of overcoming these problems is to mount the mower on castor wheels which are capable of swiveling freely through 360.degree.. This enables the lawn mower to be maneuvered in any direction, in a forward/rearward direction, sideways, diagonally, rotationally etc. This makes the lawn mower highly maneuverable and furthermore, it obviates the need for the operator to raise the wheels off the ground when he wishes to change direction. However, such maneuverability may not be desirable in certain circumstances. For instance, if an operator is using the mower on the side of a hill or bank and the operator wishes to traverse along the side of the hill or bank in a straight line with the mower, the operator would have to use considerable effort to maintain the direction of travel of the mower in a straight line and to prevent the mower from sliding sideways down the hill or bank.
It is therefore desirable to have a lawn mower which is able to be changed between two modes of operation, a first mode where the mower is able to move in any direction both linearly and rotationally i.e. the wheels can freely swivel to any direction of travel, and a second mode where the mower is only able to move in a forward or rearward direction only i.e. the wheels have a fixed direction of travel
U.S. Pat. No. 5,653,096 discloses such a mower. The cutting deck of the mower is mounted on three castor wheels. In its first mode of operation, the castor wheels are able to swivel freely enabling the mower to be maneuvered in any direction. In its second mode of operation, the direction of travel of the two rear castor wheels of the mower can be locked in a forward/reverse direction or sideways direction. While the direction of travel of the two rear wheels is fixed, the mower is only able to travel in either a forward/reverse direction or a sideways direction.
The locking mechanism disclosed in U.S. Pat. No. 5,653,096 for each rear castor wheel comprises a locking pin mounted on the cutting deck close to the castor wheel. Corresponding holes, which are capable of receiving the locking pin, are formed in the castor wheel. In the first mode of operation the pin is held away from the holes. The castor wheel is able to freely swivel through 360.degree.. However, when one of the holes in the castor wheel is aligned with the locking pin and the locking pin is moved such that it engages with the hole, the castor wheel is prevented from swiveling, its direction of travel being fixed. The direction of travel of the castor wheel is determined by the position of the hole on the castor wheel.
However, the locking mechanism disclosed in U.S. Pat. No. 5,653,096 suffers from a number of problems. Firstly, the operator has to manually orient each of the castor wheels individually so that the pin and holes become aligned. Secondly, the operator has to bend down in order to grasp the pin in order to either lock or unlock each of the castor wheels individually. This would cause problems for an operator who suffers from back problems. Furthermore, the operator is required to place his hands close to the cutting blade while locking or unlocking the castor wheel, thus putting the operator at unnecessary risk. Fourthly, as the direction of travel of the castor wheel must be fixed with some reasonable accuracy, the diameter of the hole must be similar to that of the pin. However, the castor wheels and hence the holes are located close to the zone swept out by the cutting blade when in use and, as such, would encounter grass cutting and other debris generated by the cutting action of the mower. When the pins are held away from the holes to allow the wheels to freely swivel, it is likely that the holes would fill up with grass cuttings and/or debris, thus preventing the pins from being inserted into the holes. In such circumstances an operator may be tempted to force the pin into the hole, which could be dangerous, particularly in view of the close proximity of the cutting blade to the castor wheel.